Semiconductor test system
A mixed signal test system for testing a semiconductor device having both an analog function and a digital function achieves improved resolution and low cost. The test system is formed of a functional test unit for testing a digital function of a device under test (DUT), an analog test unit (ATU) for testing an analog function of the DUT, and a synchronous control unit for synchronizing operations between the functional test unit and the analog test unit. The analog test unit includes a digitizer for converting an analog output of the DUT into a digital signal, and an acquisition memory for storing the digital signal from the digitizer in specified addresses. The wave form of the analog output is repeated by a plurality of cycles and a sampling clock for the digitizer is phase shifted by a predetermined amount for each cycle.
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This invention relates to a semiconductor test system for testing semiconductor devices such as mixed signal ICs and LSIs, and more particularly, to a semiconductor test system having a digitizer for continuously performing AD conversion of an analog signal from a device under test where an equivalent sampling frequency in the AD conversion is substantially increased.
BACKGROUND OF THE INVENTIONIn testing semiconductor devices such as ICs and LSIs by a semiconductor test system, such as an IC tester, a semiconductor IC device to be tested is provided with test signals produced by an IC tester at its appropriate tester pins (channels) at predetermined test timings. The IC tester receives output signals from the IC device under test generated in response to the test signals. The output signals are strobed by strobe signals with predetermined timings to be compared with expected data to determine whether or not the IC device properly performs the intended functions. This is a basic process for testing a logic device by a semiconductor test system.
A semiconductor device to be tested may also include analog functional blocks such as an AD converter and/or a DA converter as well as a digital functional block. Such a semiconductor device is sometimes called a mixed signal IC. An example of such a mixed signal IC is a semiconductor integrated circuit designed for modems, audio and/or video devices, and the like.
An example of semiconductor test system for testing such a mixed signal IC device (mixed signal test system) in the conventional technology is shown in
In
The timing generator TG generates timing signals such as a rate clock to synchronize the timing of the functional test unit and provides the timing pulses to the pattern generator SQPG. The test pattern generator SQPG generates a test pattern based on a test program in response to the rate clock from the timing generator TG. The timing generator TG also generates timing data and wave form data to be used in the format controller FC to produce tester rates, delay timings and wave forms in the test pattern. The test pattern at the output of the format controller FC is provided to the DUT through a pin electronics PE.
The synchronous control unit 40, although not shown, includes an event master and a digital/analog synchronous controller. In receiving signals generated by the pattern generator SQPG, the synchronous control unit 40 produces a start signal and a trigger signal to be provided to the analog test unit (ATU). The start signal and trigger signal are used to synchronize test patterns generated by the functional test unit FTU and test signals generated by the analog test unit and measurement timings in the analog test unit. A clock generator 48 receives clock signals such as the rate clock from the timing generator TG and a clock from a synthesized signal generator (SSG) in the analog test unit to produce appropriate clock signals to be used in the analog test unit (ATU).
In the example of
Plural sets of the above listed resources may be provided in the analog test unit for performing signal generation and signal measurements in response to the synchronous signal from the synchronous control unit 40. The analog test unit and the terminal pins of the DUT are connected through the pin electronics (PE).
The filter 60 is an antialiasing filter which is typically a low pass filter to prevent aliasing effects involved in a sampling process. A plurality of such filters with different pass band frequencies may be selectively used depending on the sampling frequencies. Typically, as an antialiasing filter, the filter 30 removes frequency components higher than ½ of the sampling frequency fc from the output signal of the DUT received through the pin electronics PE. The output of the filter 60 is provided to the AD converter 30.
The AD converter 30 samples an input signal from the filter 60 at each edge of the sampling clock 40clk having a sampling frequency fc and converts the sampled voltage to a digital signal, i.e., code data 30s. The code data 30s is stored in the acquisition memory (AQM) 50 in response to a memory timing signal 47s from the synchronous control unit 40. The stored data in the acquisition memory (AQM) 50 is used for signal analysis and evaluation such as by the digital signal processor (DSP) 64.
Since high resolution data can be obtained by increasing the number of sampling points, generally, a digitizer uses a highest possible sampling frequency to achieve both high even higher than the highest sampling frequency of an AD converter, an example of circuit arrangement such as shown is
Namely, the digitizer of
The multiplexer 35 receives the digitized codes from the first and second AD converters 31 and 32 and alternately selects the codes at the timing of each rising edge and falling edge of the square clock signal 45s having the same repetition rate as that of the sampling clocks 41clk and 42clk. The clock signal 45s has a square shape so as to have the same time interval between any adjoining two edges. Thus, an output signal 35s of the multiplexer 35 has an equivalent sampling frequency fce which is two times higher than the clock rate of the first or second sampling clock.
In the example of
In the conventional technology, however, to increase the overall sampling rate, the number of circuit components such as AD converters increases in proportion to the increase of the sampling rate. As a consequence, in the conventional technology involving the interleave method, there is a problem that the circuit size and cost of the digitizer increases with the increase of the sampling rate.
SUMMARY OF THE INVENTIONIt is, therefore, an object of the present invention to provide a digitizer which is capable of increasing an equivalent sampling rate without involving any substantial increase in the circuit components.
It is another object of the present invention to provide a digitizer which is capable of increasing an equivalent total sampling rate with using a single AD converter and without increasing a frequency of a sampling clock to an AD converter.
It is a further object of the present invention to provide a mixed signal semiconductor test system which is capable of converting an analog output signal of a device under test to a digital signal with high conversion speed and high resolution.
It is a further object of the present invention to provide a mixed signal semiconductor test system which is capable of converting an analog output signal of a device under test to a digital signal with high conversion speed and high resolution and storing the digital signal in a memory at a predetermined address sequence.
In the present invention, the mixed signal test system for testing a semiconductor device having both an analog function and a digital function is comprised of a functional test unit for testing a digital function of a device under test (DUT) by providing a logic test pattern to the DUT and evaluating a response output of the DUT, an analog test unit for testing an analog function of the DUT by providing a test signal to the DUT and evaluating an analog output of the DUT, and a synchronous control unit for synchronizing operations between the functional test unit and the analog test unit, wherein the analog test unit includes a digitizer for converting the analog output of the DUT whose wave form in a fixed time period T is repeated by a plurality of cycles into a digital signal wherein a sampling clock for sampling the analog output is phase shifted by a predetermined amount for each cycle, and an acquisition memory for storing the digital signal from the digitizer in specified addresses thereof.
In another aspect of the present invention, an address generator is provided to generate address data in a predetermined order to store the digital data from the digitizer in the continuous addresses of the acquisition memory in the order of sampling points on the analog output with a difference of the phase shift.
According to the present invention, an input analog signal which repeats the same wave form in the time period T by M cycles is sampled by the digitizer for the M cycles wherein a phase of the sampling clock is shifted by a predetermined amount ΔP (delta phase) for each cycle. As a result, the data obtained in the AD conversion process of the present invention shows resolution M times higher than that obtained in the normal AD conversion, i.e., an equivalent ;sampling frequency is increased by M times. Therefore, a digitizer of high resolution and high speed is achieved without using a plurality of AD converters or a higher frequency sampling clock. Accordingly, the mixed signal test system having a high performance digitizer is realized with low cost and small circuits size.
An embodiment of the present invention is shown in
This invention is based on the fact that, almost always, a wave form of a time period T shown in
The wave form of the input analog signal and a timing relationship in the digitizer used in the mixed signal test system of
Even though such timings between the analog input signal and the test system are not synchronized, the present invention of shifting the phase of the sampling clock is still feasible. For example, if the test system can measure each time period (time length of one cycle) of the analog signal such as by a time measurement unit (TMU) of
In the example of
The controller 15 provides information regarding an amount of phase shift, or delta phase ΔP (FIG. 2A and 10B), to the phase shifter 20. The delta phase ΔP is added to the phase of the sampling clock 40clk in the next cycle (period) T. In the example of
In receiving the sampling clock 40clk and the constant period signal 40s from the synchronous control unit 40 as well as the phase shift information “M” from the controller 15, the phase shifter 20 produces a phase shifted sampling clock 20clk for the AD converter 30. The phase shifter 20 produces the sampling clock 20clk by adding the delta phase shift ΔP at each period T to the sampling clock of the previous period. Namely, in the case where the input analog signal of a time period T is AD converted for M cycles, the delta phase ΔP is 360°/M. For example, if M is 8, 360°/8=45°, thus, in the first period T, the phase shift is zero, while in the second period T, the phase shift is 45°, and in the following periods, the respective phase shifts are 90°, 135°, 180°, . . . 360°.
In this manner, the phase, of the sampling clock is shifted by the unit of the delta phase ΔP at each period T of the analog signal. The output of the AD converter 30 is stored in the acquisition memory (AQM) 50 for the analysis in the later stages of the test system. The above noted operation in the digitizer DGT of the present invention is equivalent to have M AD converters in parallel and combine the digital outputs to form a serial form. Thus, the overall sampling rate of the digitizer DGT is increased by M times.
It should be noted that, for the present invention be effective, the analog output signal of the DUT with the constant time period T must repeat for M cycles. As can be seen in the foregoing, the smaller the delta phase ΔP, the higher the sampling rate and sampling resolution it becomes. However, for such a small delta phase ΔP, a sample and hold circuit (not shown) included in the AD converter 30 must be capable of high performance such as high voltage accuracy.
An example of basic configuration of the phase shifter 20 is shown in FIG. 3. In this example, the phase shifter 20 is comprised of a frequency multiplier 22 and a frequency divider 24 connected in series. The frequency multiplier 22 multiplies the frequency of the sampling clock 40clk by M times and the frequency divider 24 divides the output frequency of the multiplier 22 by M to form the sampling clock 20clk for the AD converter 30. The controller 15 provides such information “M” to the frequency multiplier 22 and the frequency divider 24.
As shown in
Timing charts of
Since the frequency of the sampling clock 20clk is unchanged, the AD converter is able to convert the input analog signal to a digital signal. Further, the sampling points on the analog signal are shifted by a 50% duty cycle, i.e, 180°, of the original sampling clock 40clk, the digital data obtained by the sum of the first cycle T1 and the second cycle T2 is equivalent to that would obtained by the sampling frequency of two times higher than the original sampling clock 40clk.
Although the digitizer in the foregoing can be most advantageously used in the mixed signal test system, other applications are also feasible. For example, the digitizer of the present invention can be used as an AD converter for an input analog signal which repeats the same wave form at least two times. By shifting the phase of the sampling clock for each of M cycles of the input signal by the phase sifter 20, an equivalent sampling rate and sampling resolution is increased by the factor of M.
The output of the digitizer DGT is stored in the acquisition memory 50 in the order of the AD conversion, i.e., from the digital data of the sampling points 11, 21, 31, . . . 81, 12, 22, 32, . . . 82 of FIG. 10A. It is also possible to store the digitized data in the order different from the above, such as 11, 12, 21, 22, 31, 32, . . . 81, 82, i.e., the order of the delta phase ΔP of the sampling points of the analog signal Si in FIG. 10A. In such a case, the digital data is stored in the acquisition memory (AQM) 50 in a manner that would be acquired by an AD converter actually having a sampling speed of M times (two times in the example of
The period counter 72 is reset to “0” at the start of operation and is incremented by one in receiving the constant period signal 40s. The period counter 72 provides an output signal 72s to an input of the second adder 78 whose other input is provided with an output of the gate circuit 76. The first adder is provided with the cycle number “M” as noted above at its one input and an output signal 79s of the register 79 at the other input. The first adder 74 thus provides the sum (accumulated data) of the two inputs to the gate circuit 76.
The gate circuit 76 sets its output to low only when the constant period signal 40s is valid (such as high) while supplies the accumulated data from the first adder 74 to the second adder 78 when the constant period signal 40s is invalid (such as low). The second adder 78 provides the sum of the output signal 72s of the period counter 72 and the accumulated data 76s from the gate circuit 76 to the register 79. In receiving the output data of the second adder 78, the register 79 generates an address signal 79s by the timing of the sampling clock 20clk.
By the arrangement described above, the address generator 70 generates address signal which accesses the acquisition memory 50 in the order of the delta phase ΔP relative to the input analog signal. Thus, the data stored in the acquisition memory 50 is in the order that would have been obtained directly by a digitizer operating by a sampling frequency of M times higher than the sampling clock 40clk or 20clk. In the above example of
The lower bit counter 82 increments by one at every constant period signal 40s to produce a lower bit signal 82s. The upper bit counter 83 increments by one at every sampling clock 20clk to produce a higher bit address signal 79H. The lower bit signal 82s is latched by the timing of the sampling clock 20clk by the flip-flop 89, thereby producing a lower bit address signal 79L. The lower bit address signal 79L and the higher bit address signal 79H are provided to the acquisition memory 50 to access the acquisition memory to store the data in the order of the phase shift ΔP in the sampling clock on the analog signal.
To summarize the address sequence generated by the address generator 70 in
To store the digitized data in the memory 50 in the order of 11, 12, 21, 22, 31, 32, . . . 81, 82, of the sampling points on the input signal Si, i.e., with the increment of the delta phase ΔP of the sampling points, the above noted address generator 70 generates the address under a formula AD=Q+(M×N). In this formula, AD is the address data generated by the address generator 70, M is a number of cycles of the analog signal used for the AD conversion, Q is a current cycle where Q=0, 1, . . . M−1, and N is a position of the sampling pulse.
In the example of
As described in the foregoing, according to the present invention, an input analog signal which repeats the same wave form in the time period T by M cycles is AD-converted for the M cycles wherein a phase of the sampling clock is shifted by a predetermined amount ΔP for each cycle. As a result, the data obtained in the AD conversion process of the present invention shows resolution M times higher than that obtained in the normal AD conversion. In other words, an equivalent sampling frequency is increased by M times. Therefore, a digitizer of high resolution and high speed is achieved without using a plurality of AD converters or a higher frequency sampling clock. Accordingly, the mixed signal test system having a high performance digitizer is realized with low cost and small circuit size.
Although only a preferred embodiment is specifically illustrated and described herein, it will be appreciated that many modifications and variations of the present invention are possible in light of the above teachings and within the purview of the appended claims without departing the spirit and intended scope of the invention.
Claims
1. A mixed signal test system for testing a semiconductor device having both an analog function and a digital function, comprising:
- a functional test unit for testing a digital function of a device under test (DUT) by providing a logic test pattern to the DUT and evaluating a response output of the DUT; an analog test unit for testing an analog function of the DUT by providing a test signal to the DUT and evaluating an analog output of the DUT; and
- a synchronous control unit for synchronizing operations between the functional test unit and the analog test unit;
- wherein the analog test unit, including: a digitizer for converting the analog output of the DUT into a digital signal wherein a wave form of the analog signal in a fixed time period T is repeated by a plurality of cycles and wherein each wave form is sampled at two or more sampling points within each-time period T by a sampling clock wherein the sampling clock for sampling the analog output is phase shifted by a predetermined amount for each cycle of the wave form; and an acquisition memory for storing the digital signal from the digitizer in addresses thereof specified by the phase shift in the sampling clock.
2. A mixed signal test system as defined in claim 1, wherein the analog test unit furthers includes an address generator for generating address data for the acquisition memory to store the digital data in continuous addresses of the acquisition memory in an order of sampling points on the wave form in the analog output corresponding to a minimum difference of the phase shift of the sampling clock.
3. A mixed signal test system as defined in claim 1, wherein the functional test unit includes a timing generator for generating timing signals for controlling timing relationships within the test system, a pattern generator for generating a test pattern, and a format controller for producing the logic test pattern based on the test pattern from the pattern generator and the timing signal from the timing generator for testing the digital function of the DUT.
4. A mixed signal test system as defined in claim 1, wherein the digitizer includes a phase shifter which produces the sampling clock whose phase is shifted at each cycle of the wave form repeated in the analog output, an analog-to-digital (AD) converter for converting the analog output of the DUT to the digital signal based on the sampling clock which is phase shifted by the phase shifter, and a controller,for controlling the amount of phase shift in the sampling clock to be produced by the phase.
5. A mixed signal test system as defined in claim 4, wherein the digitizer further includes a low pass filter for removing frequency components higher than a predetermined frequency which is a function of a frequency of the sampling clock.
6. A mixed signal test system as defined in claim 4, wherein the phase shifter produces the phase shifted sampling clock based on a clock signal from the synchronous control unit and information from the controller regarding a number of cycles of the wave form repeated in the analog output for which AD conversion by the AD converter is conducted.
7. A mixed signal test system as defined in claim 6, wherein the phase shifter includes a frequency multiplier for multiplying a frequency of the clock signal from the synchronous control unit and a frequency divider for dividing an output frequency of the frequency multiplier by the number of cycles provided from the controller wherein an operation of the frequency divider is disabled for one cycle of the output frequency of the frequency multiplier at a start of each cycle of the wave form repeated in the analog output for which the AD conversion is performed.
8. A mixed signal test system for testing a semiconductor device having both an analog function and a digital function, comprising:
- a functional test unit for testing a digital function of a device under test (DUT) by providing a logic test pattern to the DUT and evaluating a response output of the DUT;
- an analog test unit for testing an analog function of the DUT by providing a test signal to the DUT and evaluating an analog output of the DUT; and
- a synchronous control unit for synchronizing operations between the functional test unit and the analog test unit;
- wherein the analog test unit, including: a digitizer for converting the analog output of the DUT into a digital signal wherein a wave form of the analog signal in a fixed time period T is repeated by a plurality of cycles and wherein each wave form is sampled at two or more sampling points within each time period T by a sampling clock wherein the sampling clock for sampling the analog output is phase shifted by a predetermined amount for each cycle of the wave form; an acquisition memory for storing the digital signal from the digitizer; and an address generator for generating address data for the acquisition memory in response to the phase shift in the sampling clock to store the digital data in continuous addresses of the acquisition memory in a predetermined order of sampling points on the wave form repeated in the analog output in such a way that the digital data is acquired by an AD converter using a sampling clock whose frequency is M times higher than the sampling clock actually used.
9. A mixed signal test system as defined in claim 8, wherein the address generator generates address data AD based on a formula AD=Q+(M×N) where M is a number of cycles of the wave form repeated in the analog signal used for the AD conversion, Q is a current cycle where Q=0, 1, M−1, and N is a position of the sampling pulse.
10. A mixed signal test system as defined in claim 8, wherein the address generator includes a period counter for counting a constant period signal from the synchronous control unit, a first adder provided with data showing the number of cycles of the wave form repeated in the analog output for which the AD conversion is performed, a gate circuit provided with the constant period signal and an output of the first adder, a second adder connected to an output of the period counter, and a register which is provided with an output of the second adder and produces the address data at timings of the phase shifted sample clock.
11. A mixed signal test system as defined in claim 8, wherein the address generator includes a lower bit counter which increments by one at every pulse of a constant period signal, an upper bit counter which increments by one at every pulse of the phase shifted sampling clock, and a flip-flop connected to an output of the lower bit counter and is provided with the phase shifted sampling clock, wherein the flip-flop produces a lower bit of the address data and the upper bit counter produces an upper bit of the address data.
12. A mixed signal test system as defined in claim 8, wherein the digitizer includes a phase shifter which produces the sampling clock whose phase is shifted at each cycle of the wave form repeated in the analog output, an analog-to-digital (AD) converter for converting the analog output of the DUT to the digital signal based on the sampling clock which is phase shifted by the phase shifter, and a controller for controlling the amount of phase shift in the sampling clock to be produced by the phase shifter.
13. A mixed signal test system as defined in claim 12, wherein the phase shifter produces the phase shifted sampling clock based on a clock signal from the synchronous control unit and information from the controller regarding a number of cycles of the wave form repeated in the analog output for which AD conversion by the AD converter is conducted.
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Type: Grant
Filed: Nov 18, 1999
Date of Patent: Feb 6, 2007
Assignee: Advantest Corp. (Tokyo)
Inventor: Koji Asami (Fukaya)
Primary Examiner: Safet Metjahic
Assistant Examiner: Jermele M. Hollington
Attorney: Muramatsu & Associates
Application Number: 09/443,021
International Classification: G01R 31/26 (20060101); G01R 31/02 (20060101); G01R 13/14 (20060101);